Strain-matched hub for motor/generator

Abstract

A strain-matched hub for a motor/generator. The motor/generator preferably includes a cylindrical rotor surrounding a stator, and of larger diameter than a shaft. The hub, formed of a single material, connects the shaft to the rotor assembly, and contains a fastener circle whose expansion is matched to the rotor's expansion, in operation. Like the rotor, the hub's fastener circle expands uniformly around the fastener circle's circumference. Typically, a ring of keystone-shaped metal elements fits the hub to the rotor. The hub attaches to the keystone-shaped elements with a plurality of bolts or other fasteners, and the keystone-shaped elements fit to the rotor. The hub is formed of a single material and contains a plurality of spokes, each spoke positioned along a radius from the center of the hub to the center of a bolt. Each spoke is shaped to fit between two pairs of tangent-joined circles. For each pair of circles, the center of the circle that is formed in part by the inner curve of the hub rim is located radially outside the center of the circle that is formed by the outer curve of the hub's center region.

I claim:  
     
       1. An electric machine, comprising: 
       a hollow cylindrical rotor, which is part of a hollow cylindrical rotor assembly, the hollow cylindrical rotor assembly having a plurality of fastener openings; and  
       a hub connecting the hollow cylindrical rotor assembly to a shaft;  
       wherein the hub comprises a hub rim connected to a hub center region by a plurality of spokes, said hub rim having a plurality of fastener openings;  
       and wherein an imaginary circle through the hub rim's fastener openings expands substantially uniformly around its circumference as the hub rotates.  
     
     
       2. An electric machine according to claim  1 , in which, at any given time during rotation of the hollow cylindrical rotor assembly and the hub, a distance of radial expansion of the hub rim's imaginary circle substantially equals a distance of radial expansion of an imaginary circle through the rotor assembly's fastener openings. 
     
     
       3. An electric machine according to claim  2 , wherein the hub is located outside the axial length of the rotor. 
     
     
       4. An electric machine according to claim  3 , in which the hub is made of a plastic material. 
     
     
       5. An electric machine according to claim  4 , in which the hub is made of a polyamideimide plastic. 
     
     
       6. An electric machine according to claim  5 , further comprising a ring of keystone-shaped metal elements that are part of the rotor assembly, the hub attaching to the keystone-shaped elements with a plurality of bolts, and the keystone-shaped elements making an interference fit to the rotor. 
     
     
       7. An electric machine according to claim  6 , in which the hub comprises a plurality of spokes, each spoke positioned along a radius from the center of the hub, and shaped to fit between two pairs of tangent-joined circles, each pair of circles including a first circle that is formed in part by the inner curve of the hub rim and a second circle that is formed in part by the outer curve of the hub's center region, the center of the first circle located radially outside the center of the second circle. 
     
     
       8. An electric machine according to claim  7 , in which the hub is formed to include one or more stress-relief holes between adjacent bolts. 
     
     
       9. An electric machine according to claim  4 , further comprising: 
       a stator, surrounded by the rotor;  
       an array of permanent magnets on the rotor that provide a uniform dipole field, such that the stator lies along the axis of the dipole field;  
       windings on the stator; and  
       an electric commutator which provides current to the windings;  
       wherein the array of permanent magnets comprises bars of identical permanent magnets assembled in a circle, wherein the bars are dipole elements, each bar of the bars having a vector direction of magnetization that rotates at a rate which is twice that of a vector, rotating about the circle, pointing from the center of the uniform dipole field to the center of the dipole elements.  
     
     
       10. An electric machine according to claim  1 , further comprising: 
       a stator, surrounded by the rotor;  
       an array of permanent magnets on the rotor that provide a uniform dipole field, such that the stator lies along the axis of the dipole field;  
       windings on the stator; and  
       an electric commutator which provides current to the windings.  
     
     
       11. An electric machine according to claim  10 , wherein the array of permanent magnets comprises bars of identical permanent magnets assembled in a circle, wherein the bars are dipole elements, each bar of the bars having a vector direction of magnetization that rotates at a rate which is twice that of a vector, rotating about the circle, pointing from the center of the uniform dipole field to the center of the dipole elements. 
     
     
       12. An electric machine according to claim  11 , wherein the electric machine is surrounded by an aluminum containment vessel. 
     
     
       13. A hub, comprising: 
       a hub center region surrounding a central hole;  
       a hub rim connected to said hub center region by a plurality of radially-directed spokes, said rim including openings for receiving fasteners;  
       the hub having the quality that a fastener circle formed by the openings expands, under high speed rotation about a shaft extending through the central hole, substantially uniformly around the fastener circle's circumference.  
     
     
       14. A hub according to claim  13 , in which the hub is made of a plastic material. 
     
     
       15. A hub according to claim  14 , in which the hub is made of a polyamideimide plastic. 
     
     
       16. A hub according to claim  15 , the hub comprising a plurality of spokes, each spoke positioned along a radius from the center of the hub, and shaped to fit between two pairs of tangent-joined circles, each pair of circles including a first circle that is formed in part by the inner curve of the hub rim and a second circle that is formed in part by the outer curve of the hub's center region, the center of the first circle located radially outside the center of the second circle. 
     
     
       17. A hub according to claim  16 , in which the hub is formed to include one or more stress-relief holes.